1. Field of the Invention
The invention relates to a controller of a DC-DC converter, and more particularly to a switching mode controller of a bulk converter.
2. Description of the Related Art
DC-DC converters have been widely used for power supply circuits. FIG. 1 shows a conventional power supply controller of a DC-DC converter. The DC-DC converter is used to convert an input direct-current (DC) voltage Vin into an output DC voltage Vout, wherein a voltage of the output voltage Vout is smaller than that of the input voltage Vin. The power supply controller is a switching mode controller such as a pulse width modulation (PWM) controller, and is implemented in an integrated circuit (IC) 110. The IC 110 comprises a PWM controller 120 and five pins 130, 132, 134, 136 and 138. The PWM controller 120 receives the input voltage Vin and the output voltage Vout via the pins 130 and 138, respectively. According to the input voltage Vin and the output voltage Vout, the PWM controller 120 generates two PWM signals S1 and S2 to control the transistors MU and ML through the pins 132 and 136, respectively. The transistor MU is coupled between the input voltage Vin and the pin 134, and has a gate coupled to the pin 132 for receiving the PWM signal S1. The transistor ML is coupled between the pin 134 and a ground GND, and has a gate coupled to the pin 136 for receiving the PWM signal S2.
Furthermore, an output inductor L is coupled between the pin 134 and an output of the DC-DC converter. In order to obtain a desired voltage value of the output voltage Vout, the PWM controller 120 receives the input voltage Vin, a signal from the output inductor L and the output voltage Vout via the pins 130, 134 and 138 of the IC 110 respectively, and then controls the PWM signals S1 and S2 according to the received signals to switch the transistors MU and ML.